Next-generation wireless communication is associated with a high data rate and a stable quality in order to provide data and multimedia service. However, this is difficult to satisfy because a signal quality degrades due to high transmission loss in buildings such as houses, offices, and apartments. In order to solve the problem in such indoor environments, more Base Stations (BSs) may be installed, or macro cells may be used in outdoor places and wireless LANs may be used in indoor places. However, this method causes a cost load to service providers and requires users to purchase dual-mode Mobile Stations (MSs). Recently, research has been conducted on a femto cell as the solution to this problem, the standardization of which is determined by the IEEE 802.16m and 3GPP2 international standardization organizations.
A femto cell is also called the next-generation femto BS. The femto cell is similar in size to a conventional wireless router, uses an allowed frequency band, has a 10-30 m service coverage with a low power of 10-100 mW, and is connected to the network of a service provider through a conventional Digital Subscriber Line (DSL) network or a cable broadband network. The femto cell may be simply installed by a user in an indoor place in a plug-and-play mode. The femto cell relieves the cost load of service providers for construction of an additional infrastructure to remove shadow regions, and enables users to use stable, high-quality communication services in indoor places at a low cost without changing MSs.
For efficient operation of the femto cell, technical problems should be solved in the interference between a macro cell and a femto cell, power control, resource allocation, physical layer synchronization, network synchronization, a handover, a frame structure, self configuration and optimization, and operation and maintenance. Among them, the most important problem is a system deterioration caused by the interference between a macro cell and a femto cell.
A transmission (Tx) power reduction and a frequency reuse may be used to solve the lack of frequency resources due to broadband data communication requirements, and a beamforming antenna with spatial directionality may be used to improve the frequency reuse factor. The beamforming concentrates energy emitted from an antenna in a specific direction. The purpose of beamforming is to transmit or receive signals in a desired direction.
What is therefore required is a method and apparatus for interference mitigation by beamforming in a heterogeneous network having a plurality of femto cells in a macro cell.